1. Field of Invention
The present invention relates generally to medical devices, systems, and methods. More particularly, the present invention provides devices, systems, and methods for positioning an article, such as a graft or catheter, in a subcutaneous tunnel between skin and muscle tissue of a patient to establish improved access to the patient""s vascular system for hemodialysis, hemofiltration, or other extracorporeal blood treatments.
Significant attention has been focused on the specific needs of vascular access for hemodialysis. Hemodialysis is generally the only treatment alternative for patients unable to receive a kidney transplant due to medical conditions, age, or absence of a donor. Hemodialysis, in part, takes up the excretory role of the kidney by drawing blood from the arterial system into a membrane separation device outside of the body, which transfers noxious substances from the blood into dialysate for disposal and returns the cleansed blood into the venous system of the patient. Hemodialysis and other extracorporeal treatment regimens that are repeated periodically, often for the lifetime of the patient, regularly utilize vascular grafts or catheters to improve blood flow characteristics. Vascular grafts, such as the Perma-Seal(trademark) graft available from Possis Medical, Inc. and the VAG(trademark) (venous arterial graft) available from Thoratec Laboratories Corporation, are permanently implanted in a subcutaneous tunnel, where one end of the graft is typically placed in an artery and the other end of the graft is typically placed in a vein so as to create an anastomosis between the two blood vessels. Access to the graft for hemodialysis is then achieved by percutaneous introduction of a needle or an access tube.
Recently, several graft designs have been proposed where the grafts are made of certain materials, such as polytetrafluoroethylene (PTFE), silicone, DACRON, polyurethane, bovine, and the like. These grafts are designed to offer immediate access to the patient""s vasculature with reduced complications of hematomas between the subcutaneous tissue and the graft, kinking, thrombosis, pseudoaneurysm formation, or infection. While vascular grafts offer great promise, one issue to be resolved for the success and practical utility of vascular grafts is effective subcutaneous placement of such articles.
Subcutaneous placement of vascular grafts can be problematic since the grafts can easily be destroyed if they are stretched longitudinally as such forces change the graft""s material properties. Previously proposed devices and methods for subcutaneously positioning a graft include attaching a graft directly onto a trailing end of a conventional tunneling tool which creates a subcutaneous path between two blood vessels. Such methods often result in significant longitudinal forces on the graft (as the graft is constantly being pulled behind the tunneler) which may potentially destroy the graft. Moreover, such protocols may result in twisting or kinking of the graft and a loose seal between the graft and the subcutaneous tissue as the tunnel created by the tunneler is typically of equal or larger diameter than the diameter of the vascular graft. A loose seal is undesirable as it makes it difficult to properly access the graft with a needle and increases the chances of hematomas, bleeding, and infection. Other proposed methods employ feeding a graft into a hollow tunneler or tube that is already positioned within the subcutaneous tunnel. Similarly, passing the graft into a hollow tube as well as removing the tube after the graft is positioned often results in significant longitudinal forces on the graft which compromise its structural integrity. In such instances, a loose seal is also created between the graft and the subcutaneous tissue as the diameter of the hollow tube will generally be greater than the diameter of the vascular graft to allow for release of the graft.
For these reasons, it would be desirable to provide devices, systems, and methods for positioning an article, such as a graft or catheter, in a subcutaneous tunnel between skin and muscle tissue of a patient to establish improved access to the patient""s vascular system for hemodialysis, hemofiltration, or other extracorporeal blood treatments. In particular, it would be desirable if such devices, systems, and methods would minimize the friction or longitudinal forces acting against the vascular graft as it is being subcutaneously positioned. It would be further desirable if such devices, systems, and methods could provide a tighter seal between the graft and the subcutaneous tissue, minimize hematomas and infections, and enhance needle accessibility of the graft for extracorporeal treatment. The placement devices, systems, and methods should also allow for rotation of the graft without kinking or twisting complications. At least some of these objectives will be met by the devices, systems, and methods of the present invention described hereinafter.
2. Description of the Background Art
U.S. Pat. No. 4,453,928 describes a catheter tunneling apparatus where a catheter is passed into a hollow tube which is already positioned within a subcutaneous tunnel by a conventional tunneler. U.S. Pat. No. 5,300,106 describes insertion and use of a tunneling tool. Vascular grafts are described in U.S. Pat. Nos. 4,409,172; 4,604,762; 4,675,361; 4,731,073; 4,861,830; 5,840,240; and 5,886,217. The full disclosures of each of the above references are incorporated herein by reference.
The present invention provides devices, systems, and methods for positioning an article, such as a graft or catheter, in a subcutaneous tunnel between skin and muscle tissue of a patient to establish improved access to the patient""s vascular system, particularly peripheral blood vessels, for performing extracorporeal treatment on circulating blood. Exemplary extracorporeal treatment procedures include hemodialysis, hemofiltration, hemodiafiltration, plasmapheresis, apheresis, and the like. In particular, the present invention provides devices, systems, and methods which minimize longitudinal forces or friction acting against the vascular graft as it is being subcutaneously positioned while still providing a tight seal between the graft and the subcutaneous tissue, which in turn minimizes hematomas, bleeding, and infections and enhances needle accessibility of the graft for extracorporeal treatment. Moreover, the devices, systems, and methods of the present invention allow for rotation of the graft without kinking or twisting complications.
According to a first aspect of the present invention, a sheath for use with a tunneling tool comprises a pair of nested tubes and a coupling element. Each nested tube has a leading end, a trailing end, and a longitudinal opening or split. The coupling element is attached to the leading ends of the nested tubes and is removably attachable to a conventional tunneling tool. The nested tubes engage the catheter, graft, or other structure to be implanted. For example, by providing an inner tube with a diameter the same as or slightly smaller than the diameter or width of the article to be implanted, the article will be gripped by the inner tube. An outer tube may then be slid over the inner tube to apply a radially inward xe2x80x9cclampingxe2x80x9d force that enhances the inner tube grip. The longitudinal splits, however, allow the tubes to be easily opened to facilitate insertion of the articles being implanted. Once the article is inserted into the sheath, the article is passed into the subcutaneous tunnel with minimal distraction. Frictionless release of the article being implanted may then be effected by removing the sheath from over the article by separating the split nested tubes within the tunnel.
The nested tubes will usually have a uniform diameter along their entire length, typically being in the range from about 1 mm to 45 mm, preferably being in the range from 3 mm to 10 mm. The lengths of the nested tubes will usually be in the range from 10 mm to 200 cm, preferably being in the range from 20 mm to 24 cm. Each longitudinal opening or split subtends a circumferential arc of the tubes in the range from about 20xc2x0 to about 190xc2x0, preferably in the range from 60xc2x0 to about 180xc2x0. The tubes may be formed from the same or different material. For example, the outer tube may be formed from a stiffer material while the inner tube is formed from a more expansible material. Suitable tube material includes polymer materials, such as polyethylene, polypropylene, and the like. The tubes may further be counter rotatable so that the openings can be aligned to open a passage therein or the openings can be staggered apart to close a passage therein. The coupling element may comprise a male connection and a female sleeve, wherein the male connection is received within the female sleeve. In some instances the male connection may be threaded and/or knurled to provide a secure coupling between the nested tubes and the tunneling tool. The male connection and female sleeve may be formed from stainless steel, plastic, or like materials.
In another aspect of the present invention, a system for positioning an article in a subcutaneous tunnel between skin and muscle tissue of a patient comprises a tunneling tool, a pair of nested tubes coupleable to a trailing end of the tunneling tool, and a flexible article which can be slidably received within the pair of nested tubes. The nested tubes, as described above, each have a leading end, a trailing end, and a longitudinal opening. The tunneling tool may be any conventional tunneler that comprises a shaft like structure suitable for creating a subcutaneous tunnel between skin and muscle tissue of a patient. Generally, the tunnel therein lies a short distance beneath the surface of the patient""s skin, typically being within 0.5 mm to 4.0 mm from the skin""s surface. The article may comprise a catheter or preferably an arteriovenous graft, such as the Perma-Seal(trademark) graft available from Possis Medical, Inc. and the VAG(trademark) graft available from Thoratec Laboratories Corporation. One end of the graft, which may optionally have a cuff or hood on an end thereof, may be placeable in a vein and the other end of the graft may be placeable in an artery so as to create an anastomosis between the two blood vessels.
The present system advantageously minimizes longitudinal forces or friction acting against the vascular graft as it is being subcutaneously positioned. In particular, the split tubes structure inhibits graft distraction as the graft is passed and released in the subcutaneous tunnel, which in turn reduces trauma to the graft and discomfort to the patient. In some instances, at least one tube may be made from a memory alloy material or have a spring mechanism attached thereto to allow for expansion of the split tubes which in turn facilitates frictionless release of the graft. Additionally, the pair of nested tubes may be serrated along longitudinal lines to accommodate gripping of serrated articles. Moreover, the sheath structure allows the graft to be rotated within the subcutaneous tunnel without kinking or twisting complications, which is of particular benefit when utilizing hooded type grafts that need to be properly aligned with a blood vessel.
The external diameter of each nested tube will generally be equal to or slightly smaller than an expanded diameter of the flexible graft. The graft will generally have a uniform expanded diameter along its entire length, typically being in the range from about 2 mm to about 50 mm, preferably from about 4 mm to 11 mm, when the graft is made operational from vessel pressure which expands the graft. Placement of the graft in a subcutaneous tunnel that is slightly smaller than the expanded diameter of the flexible graft provides a tight and secure fit between the subcutaneous tissue and the graft. This in turn minimizes occurrences of hematomas, bleeding, and infections and enhances needle accessibility of the graft for extracorporeal treatment. The length of the graft will usually be in the range from 20 mm to 210 cm, preferably being in the range from 30 mm to 25 cm. The graft may also be trimmed to length after placement so that it is sufficiently long for the intended use. The grafts will be formed from polytetrafluoroethylene (PTFE), silicone, DACRON, polyurethane, bovine, and like materials.
In yet another aspect of the present invention, methods for subcutaneously positioning an article generally comprise providing a trailing sheath, inserting the article into the trailing sheath, and coupling the trailing sheath to a trailing end of a tunneling tool. The tunneling tool is then subcutaneously passed through the patient tissue to position the article at a desired location. The trailing sheath is then removed from over the article while the article remains at the desired location. The trailing sheath, as described above, comprises a pair of nested tubes wherein each tube has a longitudinal opening or split.
Near frictionless placement of the article at the desired location may be carried out in several fashions. For example, removing may comprise withdrawing the sheath tubes sequentially from the tunnel. Preferably, an outer tube is completely removed first from either an entrance or exit site of the tunnel followed by removal of an inner tube from the entrance or exit site. In some instances, the inner tube may be formed from a memory alloy material so that it at least partially expands after the outer tube is removed to further facilitate frictionless release of the article at the desired location. Optionally, removing may comprise withdrawing the tubes simultaneously from the tunnel in opposite directions. Still further, the tubes may be counter rotated so that the article is completely encompassed within the sheath prior to passing the tunneling tool through the patient tissue. The openings are then aligned prior to removing the sheath so that the graft remains in tact at the desired location while the sheath is removed. Any of the above protocols allow the split tubes sheath to protect the graft against longitudinal forces as the graft is subcutaneously passed and released within the tunnel. Typically, the tunneling tool will be uncoupled from the trailing sheath prior to removing the sheath. The sheath may further be rotated so that the article can be alignable with an artery or vein prior to removing the sheath. The trailing sheath may also have expansion capabilities while still encompassing the article completely prior to removing the sheath.
In still another aspect of the present invention, methods for positioning an article in a subcutaneous tunnel may comprise providing a trailing sheath having a pair of nested tubes wherein each tube has a longitudinal opening. The article is inserted into the trailing sheath and the trailing sheath is coupled to a trailing end of a tunneling tool. The tunneling tool is then subcutaneously passed through the patient tissue to position the article at a desired location. The trailing sheath is then removed from over the article while the article remains at the desired location by separating the nested tubes within the tunnel.
A further understanding of the nature and advantages of the present invention will become apparent by reference to the remaining portions of the specification and drawings.